1. Field of the Invention
The present invention relates to ink jet printing and, more particularly, to an ink jet printer having a single reciprocating jet which concurrently sweeps droplets in a direction perpendicular to the jet reciprocating direction while the jet reciprocates to print full pages of information one swath at a time. The ink jet printer has a height control sensor for maintaining predetermined spacing between swaths of printed information.
2. Description of the Prior Art
U.S. Pat. Nos. 3,465,350 and 3,465,351 to R. I. Keur et al. and U.S. Pat. No. 3,555,558 to Sherman disclose ink droplet printing devices in which an ink nozzle is moved perpnedicularly to the movement of web. Ink droplet placement is controlled by an electric field and unnecessary drops are deflected to a waste reservoir. Circuitry is provided to ensure that the droplets are charged in phase with data or video signals and that carriage motion variables are connected to ensure a uniform margin.
U.S. Pat. No. 3,737,914 to Hertz discloses a multi-jet printer whose printing head is moved from side-to-side, while the recording mechanism is moved in a direction perpendicular to that of the head movement. U.S. Pat. No. 4,050,075 to Hertz et al. discloses an ink jet writing system mounted on a travelling carriage, the carriage and recording medium being selectively moved to effect relative movement between them.
U.S. Pat. No. 4,178,595 to Jinnai et al. and U.S. Pat. No. 4,313,684 to Tazaki et al. disclose ink jet printers with oscillating print heads but are of the type which use drops-on-demand rather than print heads which emit continuous streams of ink that are concurrently broken into droplets and charged for deflection by an electrostatic field to the proper location on a receiving surface or to a gutter for recirculation.
U.S. Pat. No. 4,293,863 to Davis et al. discloses a printing device having an oscillating print head with a plurality of ink emitting nozzles and a recording medium that is mounted on a rotatable drum. The printing head is moved in either direction at a uniform velocity parallel to the area of rotation of the drum, thus printing along helical print lines or the print head may be moved a discrete distance after each rotation of the drum such that the print lines are circumferential. Several revolutions of the drum are necessary to print a line of complete fonts.
U.S. Pat. No. 3,769,630 to J. D. Hill et al. discloses an ink jet system wherein the droplets not required for printing are directed to a first gutter where the charges on the collected droplets develop a current that is sensed in an electronic feedback loop for sysnchronization of the droplet formation with droplet charging. An auxilliary gutter is positioned to receive droplets during a checking interval when a relatively high charge is applied to the unused droplets.
U.S. Pat. No. 4,255,754 to P. A. Crean et al. discloses the use of paired photodetectors to sense ink drops, one each for two output fibers, that are used to generate an electrical zero crossing signal. The zero crossing signal is used to indicate alignment or misalignment of a drop relative to the bisector of the distance between two output fibers. The sensor of this patent employs one input optical fiber and at least two output optical fibers. The free ends of the fibers are spaced a small distance from each other; the free end of the input fiber is on one side of the flight path of the drops and the free ends of the output fibers are on the opposite side. The remote end of the input fiber is coupled to a light source, such as an infrared light emitting diode (LED). The remote ends of each output fiber are coupled to separate photodetectors such as, for example, a photodiode responsive to infrared radiation. The ink is substantially a dye dissolved in water and is, of course, transparent to the infrared, thus reducing the problems of contamination usually associated with ink drop sensors. The photodiodes are coupled to differential amplifiers, so that the output of the amplifiers are measurements of the location of drops relative to the bisector of the distance between the output fiber ends confronting their associated input fibers and drops passing therebetween. Amplifier outputs are used in servo loops to position subsequently generated drops to the bisector location. The zero crossing may be used, depending upon its orientation with respect to the drop stream direction, as a time reference to measure the velocity of the drop. Therefore, the drop velocity information may be used in a servo loop to achieve a desired velocity.
The sensor of this invention uses a sensor similar to the one in U.S. Pat. No. 4,255,754, though the use and purpose is different, and the disclosure of this patent is incorporated by reference herein.
U.S. Pat. No. 3,886,564 to H. E. Naylor et al. discloses the use of differentially sensed, capacitive sensors to determine when a drop passing therebetween is equally distant therefrom, and such a sensor may be used to determine height and placement of drops in an ink stream.
U.S. Pat. No. 3,992,713 to J. M. Carmichael et al. discloses a sensor for synchronizing the drop break-off time to the charge applied by the charge electrode by using a pedestal voltage level rather than by referencing the charge level to zero, thus enabling the charge pulses to reach the required levels more quickly and accurately. This synchronizing sensor is located to one side of the carriage printer.
U.S. Pat. No. 4,063,253 to S. Ito et al. discloses a sensor and circuitry to detect ink drops for a predetermined time period and indicating improper operation if this should occur. The disorder sensed in the recording operation may be indicated by energizing a light or stopping the recording.
U.S. Pat. No. 4,136,345 to M. H. Neville et al discloses the placement of several spaced apart serially arranged sensors which are positioned in a sensing plane parallel to the deflection plane of the ink drops. One of the sensors is positioned for sensing ink drops after deflection. Timing means are connected to the sensors to compare the time of occurrence of a drop sensed between two sensors and a third one to indicate whether the drop being sensed is high or low relative to a predetermined optimum height of the drop.
U.S. Pat. No. 4,328,504 to H. Weber et al. discloses a sensor and circuitry for sensing ink drops after impacting the recording medium and comparing the sensor signals to desired signals for correcting the printing.
U.S. Pat. No. 4,333,083 to S. F. Aldridge discloses a plurality of spaced conductive members on opposite sides of an ink jet stream and having an amplifier circuit connected thereto to develop an output signal in response to the passage of charged drops. The output signal is processed to measure flight time.
None of the above references optically sense one or more of the upper and lower droplets in one vertical column sweep of droplets that normally print horizontal swaths of information one swath at a time from a single reciprocating jet and, in response thereto, determine and compare the interdroplet spacing of the ink droplets to a desired spacing. Any difference between the determined spacing and the desired spacing is indicative of correction required. At least one of the printer operating parameters is adjusted to maintain the correct interdroplet spacing for proper stitching between the printed and subsequently printed swaths based on the comparison.